The dynamics of 3-minute wavefronts and their relation to sunspot magnetic fields

TL;DR

This study analyzes 3-minute wavefronts in a sunspot, revealing their spatial, frequency, and magnetic field relationships, and introduces a new digital technique for spectral analysis of solar wave processes.

Contribution

It presents a novel combination of pixelised wavelet filtering and empirical mode decomposition to study wave dynamics in sunspots, linking wavefront structures to magnetic field inhomogeneities.

Findings

Wave motion occurs along a preferential direction.

Broadband wavefronts are composed of narrowband oscillation sources.

Wavefronts exhibit spatial and frequency fragmentation.

Abstract

We present a study of wave processes occurring in solar active region NOAA 11131 on 2010 December 10, captured by the Solar Dynamics Observatory in the 1600A, 304A, and 171A channels. For spectral analysis we employed pixelised wavelet filtering together with a developed digital technique based on empirical mode decomposition. We studied the 3-minute wave dynamics to obtain relationships with the magnetic structuring of the underlying sunspot. We found that during development of wave trains the motion path occurred along a preferential direction, and that the broadband wavefronts can be represented as a set of separate narrowband oscillation sources. These sources become visible as the waves pass through the umbral inhomogeneities caused by the differing magnetic field inclination angles. We found the spatial and frequency fragmentation of wavefronts, and deduced that the combination of narrowband spherical and linear parts of the wavefronts provide the observed spirality. Maps of the magnetic field inclination angles confirm this assumption. We detect the activation of umbral structures as the increasing of oscillations in the sources along the front ridge. Their temporal dynamics are associated with the occurrence of umbral flashes. Spatial localisation of the sources is stable over time and depends on the oscillation period. We propose that these sources are the result of wave paths along the loops extending outwards from the magnetic bundles of the umbra.